Contents lists available at ScienceDirect Comparative Biochemistry and Physiology, Part A journal homepage: www.elsevier.com/locate/cbpa Exploring relationships between cardiovascular activity and parental care behavior in nesting smallmouth bass: A field study using heart rate biologgers Tanya S. Prystay a, ⁎ , Michael J. Lawrence a , Aaron J. Zolderdo a , Jacob W. Brownscombe a , Robert de Bruijn a , Erika J. Eliason b , Steven J. Cooke a a Fish Ecology and Conservation Physiology Laboratory, Department of Biology and Institute of Environmental and Interdisciplinary Science, Carleton University, Ottawa K1S 5B6, Canada b Department of Ecology, Evolution, and Marine Biology, University of California Santa Barbara, Santa Barbara, CA 93106, USA ARTICLE INFO Keywords: Behavior Diel variation Fitness Heart rate Individual variation Parental care Physiological capacity Physiological performance Reproductive fitness Smallmouth bass ABSTRACT Research in a variety of vertebrate taxa has found that cardiac function is a major limiting factor in the ability of animals to cope with physiological challenges, and thus is suggested to play an important role in mediating fitness-related behaviors in the wild. Yet, there remains a paucity of empirical assessments of the relationships between physiological performance and biological fitness in wild animals, partially due to challenges in mea- suring these metrics remotely. Using male smallmouth bass (Micropterus dolomieu) as a model, we tested for relationships between cardiac performance (measured using heart rate biologgers) and fitness-related behaviors (assessed using videography and snorkeler observations) in the wild during the parental care period. Our results showed that heart rates were not significantly related to any measured parental care behaviors (e.g., nest tending) except for individual aggression level. After accounting for the effect of water temperature on heart rate, we found within-individual heart rate differed between days and also differed between nights. There was, however, evidence of diel variation in heart rate, where heart rate was higher during the day than at night. Although fitness is thought to be dependent on physiological capacity for exercise in wild animals, inter-in- dividual variation in heart rate alone does not appear to relate to parental care behavior in smallmouth bass at the temporal scales examined here (i.e., hours to days). Further studies are required to confirm relationships between physiological performance and parental care behavior to elucidate the apparently complex relation- ships between physiology, behavior, and fitness in wild animals. 1. Introduction Many wild vertebrates engage in parental care as a reproductive strategy to maximize offspring survival (Clutton-Brock, 1991; Klug and Bonsall, 2014). During the parental care period, individuals are fre- quently exposed to intense physical exercise, a lack of energy intake via foraging, and increased exposure to predators (e.g. Roff, 1983; Bustnes and Erikstad, 1991; Magnhagen, 1991). Research on various vertebrate taxa has suggested that energy demanding behaviors, such as those associated with parental care behaviors, rely strongly on aerobic scope and energy acquisition and utilization (Priede, 1977; Reardon and Chapman, 2010; discussed in Brownscombe et al., 2017). Cardiac function likely mediates parental care behavior and fitness given its relationship with oxygen delivery and metabolism (Mirkovic and Rombough, 1998) and circulation of signaling molecules (i.e. hor- mones), which are known to affect parental care (e.g. Dey et al., 2010). In fish, oxygen delivery to tissues, required to synthesize ATP (energy), is limited by the performance of the cardiovascular system (reviewed in Farrell et al., 2009; Eliason et al., 2013). Oxygen consumption increases with exercise (Ji, 1999; Farrell, 2009; Eliason et al., 2013), which is regulated through adjustments in cardiac output and arteriovenous oxygen difference (Farrell et al., 2009; discussed in Eliason and Antilla, 2017). Cardiac output is a function of heart rate (f H ) and stroke volume. Yet in some species, including centrarchids, stroke volume has been found to remain relatively constant in various situations. For instance, when exhibiting temperature stress, smallmouth bass f H and cardiac output increased while resting stroke volume remained unaffected (Schreer et al., 2001). These same trends were also reported in studies https://doi.org/10.1016/j.cbpa.2019.04.012 Received 18 October 2018; Received in revised form 8 April 2019; Accepted 11 April 2019 ⁎ Corresponding author at: Department of Biology, Carleton University, Ottawa, ON K1S 5B6, Canada. E-mail address: tprystay@gmail.com (T.S. Prystay). Comparative Biochemistry and Physiology, Part A 234 (2019) 18–27 Available online 18 April 2019 1095-6433/ © 2019 Published by Elsevier Inc. T